1. Field of the Invention
The invention relates to a connecting assembly suitable for use in a propeller shaft of the driveline of a motor vehicle. The assembly comprising a tubular shaft, preferably made of a composite material, and a connecting piece positioned coaxially relative to an end of the tubular shaft, the shaft and the connecting piece having connecting means which inter-fit with one another in the circumferential direction so that drive can be transmitted.
2. Description of Prior Art
From West German Patent Specification No. 30 07 896, there is known a connecting assembly of the said type in which the end of the tubular shaft is slid on to the connecting piece which is provided with outer teeth, with the teeth cutting into the tube surface. The outside of the connection is secured by an annular member safeguarding the assembly.
From West German Patent Specification No. 38 28 018, there is known a connecting assembly in which, again, a metallic connecting piece with outer teeth is pressed into the end of a fibre composite tubular shaft with the teeth cutting into the composite material and with the end of the shaft radially expanded. In the region adjacent the pressed-in connecting piece (which at the same time serves as a joint part) the cross-section of the fibre composite tube is reduced.
Furthermore, from US Patent Specification No. 4,722,717, there is known a connecting assembly between the open end of a fibre composite tubular shaft and a connecting piece in which complementary longitudinal and circumferential grooves are provided on the inner face of the shaft end and on the outer face of the inserted connecting piece, which grooves are filled with a hardenable resin which may contain short fibre parts so that after hardening of the resin a connecting member providing a form-fitting connection in the circumferential and axial directions is formed.
In the latter case, it is the intention to provide a connection between the end of the shaft and the connecting piece which may not only be torque-loaded but which is also axially firm. Because of their specific designs, the first two above-mentioned assemblies may also be subjected to high loads, or at least compressive forces, both in the circumferential and axial directions.
The deformation behaviour in the case of a frontal impact of a modern motor vehicle is specified from the point of view of design in such a way that certain progressive characteristic deformation curves are achieved.
When using the above-mentioned connecting assemblies in longitudinal driveshafts (propeller shafts) of motor vehicles with rear wheel drive or four wheel drive it has been found to be highly disadvantageous that fibre composite shafts or other lightweight shafts which, as a rule, may do without an intermediate joint because of their low weight, are characterised by a very high degree of stiffness. In the case of a frontal impact, the stiff propeller shaft and the mass inertia of the connected driving axle and differential causes the crush zone of the vehicle to be stiffened and to lose its protective effect for the passengers in the vehicle. The energy absorption conditions as specified are upset by the connection between the rear axle masses and the vehicle front through the propeller shaft and in consequence, the passenger bodies are braked too suddenly. In the case of an accident, this may lead to serious injuries or even death.
Furthermore, crash tests have demonstrated that even a safety device in the form of an air bag is adversely affected by the described effect of the stiff propeller shaft. In consequence, the air bags become effective at too late a stage, and again passengers do not receive the necessary protection.